Self lubricating powder metal bearings have been manufactured by the powder metal industry since the 1930's. These bearing are traditionally compacted from bronze metal powder, sintered, and then impregnated with a lubricating oil. A sealed self lubricating bearing releases lubricating oil as the bearing heats from friction, and then absorbs the oil back into the porosity of the bearing after it cools. The advent of copper ferrous alloys in the 1940's allowed the manufacture of self lubricating powder metal bearings which are made of steel, and can be heat treated for high wear and high compressive strength applications. These bearings are compacted from iron copper alloy powders, sintered, heat treated, tempered, and then impregnated with the lubricating oil.
A drawback to self lubricating bearing sleeves that have heretofore been used is that a liquid can became absorbed in the porous powdered metal bearing sleeve during its manufacture prior to impregnating the bearing sleeve with the lubricant. In particular, in order to strengthen the powdered metal bearing sleeve, the bearing sleeve may be quenched in oil during a heat treatment process. While the heat treatment process significantly strengthens the bearing sleeve, the quench oil is absorbed into the pores of the powered metal structure. A drawback to absorbing quench oil into the pores is that the quench oil occupies volume within the pores that would otherwise be impregnated with lubricant.
One method of removing the quench oil is to heat the bearing sleeve in a furnace to combust the quench oil within the pores. However, combusting the quench oil has the drawback of creating smoke and fires within the furnace. The smoke and fire are not only inconvenient, but also releases a significant amount of pollution into the environment. In addition, the combustion of the quench oil within the pores leaves residual combustion products within the pores. These residual combustion products can significantly reduce the volume of the pores. A drawback to the reduced pore volume is that the amount of lubricant that can subsequently be absorbed by the powdered metal bearing sleeve is reduced thereby decreasing the effectiveness of the self lubricating bearing sleeve.
What is needed therefore is a method and apparatus for removing quench oil from a powdered metal bearing sleeve which overcomes the above-mentioned drawbacks.